This application claims the priority of German Patent Document 100 28 147.8, filed Jun. 7, 2000, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a process for operating a workpiece transport system for a press arrangement and to a system for implementing the process.
The braking devices used in known processes have the purpose of avoiding, at the point in time at which the press arrangement is not operating, the risks resulting from the potential energy of lifting parts of such systems or from the energy of the counterweight because of a possible movement of the parts downward or upward. Such devices, which are also called holding brakes, have friction linings which are designed such that they can carry out only a limited number of operational brakings; that is, brakings while in motion, because constructively they are not designed for this purpose. Such operational brakings may be necessary, for example, as a result of power failure or faulty connections during the start of the operation.
As the wear of the friction linings of the braking devices increases, however, the braking torque which can be applied decreases. Thereby a secure holding of the system parts is no longer ensured, and the potential energy of these parts represents a danger.
As an alternative, knows mechanical holding devices are used which have a form fit with respect to the respective system part. However, the manufacturing of these holding devices requires relatively high expenditures, and these holding devices must be adapted separately to each system. Therefore, relatively high costs are incurred.
In contrast, the normally used, above-described braking devices are standard parts, which result in relatively low costs and very low mounting expenditures. Another advantage of the known braking devices is the lower required braking torque because the braking device is usually followed by a gearing down of the drive and thus an increase of the torque.
With respect to the general prior art concerning braking devices in the case of workpiece transport systems for press arrangements as well as processes for operating workpiece transport systems for press arrangements, reference is made to CH-PS 291 869 and EP 0 511 028 B1.
An object of the present invention is to provide a process for operating a workpiece transport system for a press arrangement, in which it is ensured in any condition during the operation of the workpiece transport system that the braking device can apply the required torque.
According to the invention, this object has been achieved by providing that the functioning of the braking device is checked by the application of a predefined torque by the driving device.
According to the invention, the checking determines whether the braking device is still operating so that it is possible to not start the process for operating the workpiece transport system for the press arrangement if the torque applied by the driving device exceeds the maximal holding moment of the braking device. As a result, a secure functioning of the braking device is ensured in every situation, and potential accidents as a result of movements of the workpiece transport system or its parts can be prevented. An enormous increase of safety in the operation of press arrangements is thereby achieved and human lives can be saved.
The predefined torque applied by the driving device is in a range which is slightly lower than the torque to be applied by the braking device. Naturally, the torque applied by the mass of the workpiece and the workpiece transport system have to be taken into account.
Another advantage of the process according to the invention resides in the fact that no additional hardware expenditures are required because standard parts can be used. As a result, the moment of inertia is advantageously also not increased.
One possibility of implementing the checking procedure of the braking device, which can be used in a particularly meaningful manner in practice, will be achieve if the predefined torque is applied by the driving device when the press arrangement is switched off. This represents no loss of time during the operation of the press arrangement and ensures a reliable operation of the braking device each time the press arrangement is switched on again.
Of course, the predefined torque by the driving device can, as an alternative, also be applied when the press arrangement is switched on or at arbitrary points in time during the stoppage of the press arrangement manually by an operator.
When the torque of the braking device is too low, corresponding measures can be taken for the purpose of personal safety. That is, the workpiece transport system and/or the press arrangement can then be switched off.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.